1. Field of the Invention
The present invention relates to a new and improved tire including a tread surface or portion.
In its more specific aspects, the present invention particularly relates to an improved tire including a tread surface or portion which comprises profile elements such as blocks, ribs and the like extending in circumferential direction. These profile elements are provided with lamella fine cut-outs or incisions defining wall regions of a non-planar configuration.
The present invention further relates to improved tire mold lamellae for producing lamella fine cut-outs or incisions in tire tread surfaces.
2. Discussion of Background and Material Information
It is known in the art that the sliding friction which occurs between the tire and the ground during normal rolling and upon braking and accelerating, plays an essential role with respect to the gripping characteristics or properties of a tire. There is always present a certain amount of skid or slip between the ground and the tire of a travelling vehicle. During braking and accelerating as well as during travel through curves the amount of skid or slip is substantially greater than during normal rolling or travel of the tire.
It is also known that reducing the skid will assist in improving the gripping and adhesion characteristics as well as the handling characteristics of the tires. Therefore, maintaining the skid at a minimum is a central aspect of tire development. The measures heretofore undertaken for this purpose, on the one hand, were carried out on with respect to the mixture composition for the tread surfaces and, on the other hand, from the standpoint of tread construction, i.e. by correspondingly structuring the tread surface profile. The contribution made thereto by the mixture composition, can be briefly summarized in that the tread surface rubber must be capable of permitting cyclic deformations during sliding of the tire upon ground irregularities in order to thereby consume part of the kinetic energy. As a constructional measure it has heretofore proven useful to form lamella fine cut-outs or incisions of a width in the range of 0.4 to about 0.8 mm. in the profile elements in order to provide additional gripping edges which contribute to reducing skid or slip. The skid reducing effect of fine cut-outs or incisions in the tire, however, is not merely the result of additional gripping edges. Above all, particularly on a dry roadway and in the presence of strong tire deformations, which also are the conditions present during a tire handling test, the mutually facing walls of the tire fine cut-outs or incisions are subject to high frictional engagement. The thus produced friction losses are taken from the kinetic energy of the tire and thus likewise act in a skid reducing manner.
However, it has been found that conventional lamella formation in the tread surface profile nevertheless causes some deterioration in handling. The reason therefore is that tire fine cut-outs or incisions always tend to render more labile or unsteady the contact geometry of the tire. At high travelling speeds this unsteadiness will be more dominant than the positive effects due to the additional gripping edges or the dissipated friction energy.
Further disadvantages which may result from tire fine cut-outs or incisions, reside in their tendency to capture stones or gravel, promoting break-outs which start from the base of the tire fine cut-outs or incisions, and irregular wear.
In order to moderate the disadvantages of fine cut-outs or incisions, it is known in the art and a frequent practice to reduce the depth of the fine cut-outs or incisions, either across the entire width of the fine cut-out or incision or only in sections thereof. This means, however, that during the service life of the tire such raised fine cut-outs or incisions are sooner or later entirely or partially lost, as a result of which there will surely result a more or less abrupt deterioration in the gripping characteristics or properties of the tires.
Furthermore, it is known in the art to use, instead of totally planar tire fine cut-outs or incisions, cut-outs or incisions which are wave or zig-zag shaped as seen in radial top plan view. In this manner, the slippage or sliding past one another of mutually facing wall halves of the fine cut-outs or incisions in lateral direction is rendered substantially more difficult. In comparison with entirely planar tire fine cut-outs or incisions there is thus obtained, above all, a handling advantage.
There are, however, also known fine cut-outs or incisions where the zig-zag or wave configuration extends into the depth of the tire. In this manner there are formed transversely oriented edges within the fine cut-outs or incisions and these are used, for example, according to German Published Patent Application No. 1,480,932 for preventing stones from penetrating or further migrating toward the radial-ply construction. Furthermore, as described, for example, in European Published Patent Application No. 0,282,765, there have been proposed mirror-image pairs of fine cut-outs or incisions containing a zig-zag configuration extending in the depth direction. The thus resulting, always mutually opposed inclination of pairs of fine cut-outs or incisions are intended to particularly improve upon the tire grip at a wet, snowy or icy roadway. Additionally, the in-depth extending zig-zag configuration further has the effect that the relative movements of the adjoining walls with respect to each other progressively decrease toward the base of the tire fine cut-outs or incisions. The risk of fissure formation at the base of the tire cut-outs or incisions is thereby suppressed and there is also diminished the tendency of irregular wear.
All heretofore existing wave or zig-zag shaped and non-planar tire fine cut-outs or incisions restrict the relative movement of the adjoining walls with respect to each other only in the direction of extent of the wave or zig-zag configuration. In a direction perpendicular thereto the walls of the fine cut-outs or incisions can be described as continuous straight wall extents.